Many products include a substrate which are coated with a particulate substance, such as fibers or granules adhering to a surface of the substrate. For example, common forms of such fibers are often referred to as flock, whereas particles, in general, may be abrasive particles, such as are used in sandpaper. Because flock usually has the largest length-to-width ratio of commonly applied particulate materials and is usually made of flexible materials, with a typical length between about thirty and eighty mils and a denier of between about one and eighteen denier, it is usually the most difficult particulate substance to deposit at high density levels.
With regard to flocked products, for example, the highest density of fibers on commercially available products, generally do not exceed about four ounces of flock per square yard. It is rarely possible to exceed about fifteen or so percent of the theoretical flock density possible for a given flock length and denier, i.e. where maximum theoretical flock density on the surface exists when the substrate is essentially packed with straight fibers, each fiber touching adjacent fibers along its whole length.
There are several problems associated with limited particulate density. For example, multiple applications of a weight or a frictional shuffling action, as on a flocked carpet, or on any of the commonly available carpet structures, often bends the fibers at the base where the fibers enter the adhesive layer or base structure, tending to break the fibers without actually abrading or wearing them away throughout their lengths.
In contrast, the same weight or shuffling action on a high-density surface bends the fibers, but not at their bases, since the close proximity of adjacent fibers "support" each other, causing the weight or abrasive force to wear the top ends of the fibers, allowing the whole length of the fibers to wear, thus presenting a great deal of material to resist the abrading action. However, an increase in the density of flock on a flocked surface will result in a substantially greater increase in the resistance of the flocked surface to abrasion than the increase of flock density would normally indicate. Hence, even the highest density flocked substrates commonly available generally do not offer adequate abrasion resistant surfaces for use in many applications.
In another embodiment, the utility of filters having flocked components is also limited by the density and arrangement of fibers of the flock. For example, a relatively low density of fibers can significantly diminish the efficiency of filtration. Also, flock is generally uniformly distributed on substrates, thereby limiting, for example, the design of filters or the esthetic design of automobile cabin interiors which employ flocked components.
Therefore, there is a need for a method of significantly increasing or varying the density of a particulate substance adhering to a substrate and for articles which are formed by such a method.